Prediction And Prevention Of Water Inrush Under The Unconsolidated And Confined Aquifer In Concealed Coalfields In North China

In North China type coalfield, the coal measure strata are generally covered by thick unconsolidated formation of Quaternary, at the bottom of which there is a confined aquifer contained non-cemented sand and gravel. With the expansion of the mining scale and the uplift of upper mining limit under the unconsolidated and confined aquifer, water inrushes from the aquifer into working faces happen from time to time, resulting in serious geological hazards and hindering the safety production in coal mines.In this paper, the south mining area of the Qidong coal mine, which is located in the Huaibei coalfiled, is used as the main study area. First of all, according to the geological and hydrogeological data in the south mining area of the Qidong coal mine, the distributed laws of the bottom aquifer (the fourth aquifer) and the bottom clay from the unconsolidated formation, the bedrock and the bedrock faults, etc. are analyzed. Then, two different kinds of water-inrush risk areas in the south mining area of Qidong coal mine, which are separately predicted by the Fisher's discriminant analysis method and the GIS-AHP (Analytic Hierarchy Process) multivariate information fusion method, are analyzed. At last, the fluid-solid coupled numerical simulation of no.61 coal seam in the south mining area of the Qidong coal mine are carried out by the discrete element software of UDEC. And combining simulated results with China's coal mining requirements, the vertical height of waterproof coal pillar of no.61 coal seam near the unconsolidated and confined aquifer, and the width of waterproof coal pillar of no.61 coal seam near the fault are both confirmed in the south mining area of the Qidong coal mine.The main conclusions from this paper are:Although the range size of two different kinds of water-inrush risk areas predicted by the Fisher's discriminant analysis method and the GIS-AHP multivariate information fusion method is different, there are still both three diffent water-inrush risk areas, which distribute orderly each other, and their locations of these three water-inrush risk areas are similar. In addition, fluid-solid coupled numerical simulation results by UDEC show that the degree of interconnection between the bed-separated and vertical fractures, and increases in hydraulic pressures and seepage rates in overlying strata are key factors in predicting potential water inrush when mining shallow coal seams under an unconsolidated, confined aquifer. Combining the numerical simulation results with China's coal mining requirements, the vertical height of waterproof coal pillar of no. 61 coal seam near the unconsolidated and confined aquifer is 90 m with the upper mining limit of an altitude of-509.36 m, and the width of waterproof coal pillar of no.61 coal seam near the fault is 30.7 m in the south mining area of the Qidong coal mine.